Electronic devices, in particular those used for two-way person-to-person communication or audio and video recording, have microphones in order to receive speech from a near-end talker, and loudspeakers in order to playback audio signals that may include speech from a far-end talker received from a far-end device. In some cases, the audio signals output by the loudspeakers include sound internally generated by the device itself, such as alerts, music, and ring-tones. Typical examples of such electronic devices include portable telecommunications devices (mobile telephones), desktop computers, laptop computers, tablet computers and audio systems for homes and vehicles. In addition, many of these devices can be used together with external devices having their own microphones and loudspeakers.
In situations where microphones of the electronic device are receiving speech at the same time that its loudspeakers are outputting audio signals, the signal output by the loudspeakers may be captured by the microphones due to the proximity of the microphones to the loudspeakers, or the playback levels in the loudspeakers, or the sensitivity of the microphones. In a two-way communication application, the output audio signal often originates at a far-end device. When this playback signal is captured by the microphone and is then sent to the far-end device for playback to the far-end user, this signal is perceived by the far-end user as an echo. Echo can be picked up simultaneously with desired speech from a near-end speaker, often degrading the quality of the desired speech and communication experience and making comprehension difficult. In addition, there can be playback signals that do not originate on the far-end device, but in the near-end device itself, such as alerts, where it is desirable that such signals be either not recorded by the near-end device or not sent to the far-end user. Effective removal of such echo originating with a far-end signal, and/or what is termed as echo in this description though originating locally in the far-end device, is of interest.